Fix crash when using invalid conditional expressions
Fix crash when using invalid conditional expressions

Fixes bug 594400.

phako/vala,tjol/vala-tjol,flobrosch/vala-fixes,Distrotech/vala,GNOME/vala,lovebug356/vala,Jc2k/vala,severinh/vala,GNOME/vala,frida/vala,themiwi/vala,tjol/vala-tjol,xdave/pvala,frida/vala,rvu95/vala,Jc2k/vala,frida/vala,GNOME/vala,lovebug356/vala,kamanashisroy/aroop,rvu95/vala,frida/vala,tjol/vala-tjol,phako/vala,playya/vala,kamanashisroy/aroop,jessevdk/vala,playya/vala,Distrotech/vala,jessevdk/vala,spidermonkdust/vala,flobrosch/vala-fixes,flobrosch/vala-fixes,playya/vala,rvu95/vala,severinh/vala,frida/vala,spidermonkdust/vala,jessevdk/vala,spidermonkdust/vala,severinh/vala,themiwi/vala,themiwi/vala,GNOME/vala,Distrotech/vala,kamanashisroy/aroop